Optically clear pressure-sensitive adhesives (OCAs) find wide applications in optical displays. Such applications include, but are not limited to, bonding polarizers to modules of a liquid crystal display (LCD) and attaching various optical films to a glass lens in mobile hand held devices (MHH). The polarizers may be in direct or indirect contact with the OCA. Furthermore, widely used touch panels, i.e., touch screens, typically include indium-tin oxide-(ITO) coated polyethylene terephthalate film or ITO-coated glass. The ITO is typically in a patterned trace form and is electro-conductive. These ITO-coated substrates are often attached to the display modules using OCAs. In some touch panel designs, the OCA can come in direct contact with the electro-conductive ITO traces. In such a case, the OCAs need to be compatible with the ITO trace, i.e., the OCA should cause no more than minimal change in the electrical resistance of the ITO trace while the OCA remains in contact with the ITO trace.
A major issue, particularly in capacitive touch screen applications, is that the ITO patterns often remain highly visible due to the refractive index mismatch between the ITO, the substrate, and, if used, an OCA. Due to the higher reflection of the ITO traces they stand out from the surrounding areas. Especially from some viewing angles and/or under specific light conditions the pattern is clearly visible, which is objected to by the device makers and their customers. In view of various attempts at solving this problem, e.g., through the use of coatings with high indices of refraction to match the index of the ITO trace, great technical challenges still remain to hide ITO traces and other electro-conductive traces.